In the development of advanced CMOS (complementary MOS) devices in which transistors have been miniaturized, a sheet resistance of a diffusion layer or a gate electrode in a source region or a drain region should be reduced in order to improve characteristics of transistors. For the purpose of reduction in sheet resistance, a salicide technique has been employed which includes bonding metal after deposition of a gate electrode material and after formation of a source/drain region, performing an annealing process to silicidate only metal attached to the gate electrode material and the source/drain region, and then removing metal that has not reacted by selectively etching.
Furthermore, deterioration of a driving current due to depletion in a gate electrode of polysilicon (poly-Si) has been a recent issue. Attempt to avoid depletion in a gate electrode has been made by applying a metal gate electrode. Pure metals, metallic compounds such as metal nitrides, silicide materials, germanium compounds, or the like have been considered as materials used for the metal gate electrode. In any case, an N-type MOSFET or a P-type MOSFET should have a threshold voltage (Vth) which can be set at a proper value.
In order to achieve Vth of ±0.5 V or less in a CMOS transistor, a gate electrode in an N-type MOSFET should use a material having a work function not more than a midgap of Si (4.6 eV), preferably not more than 4.4 eV, and a gate electrode in a P-type MOSFET should use a material having a work function not less than a midgap of Si (4.6 eV), preferably not less than 4.8 eV. Thus, technology to form a metallic compound layer having an optimum resistance or work function has been demanded for a source/drain region, a gate electrode for an N-type MOSFET, and a gate electrode for a P-type MOSFET. Furthermore, increase in fineness and complexity of element structures has required a method of forming a metallic compound layer uniformly on a large area with excellent covering capability.
Examination has heretofore been made of a method of forming a silicide layer among other metallic compound layers. In the technology disclosed in J. Vac. Sci. Technol. B19(6), November/December 2001 L2026 (hereinafter referred to as Non-patent Document), a Ni layer is formed on a polysilicon gate pattern by a sputtering method, and then annealing treatment is performed so that the Ni layer reacts with polysilicon to form a silicide layer. In the case, the composition of the silicide can be controlled by an annealing temperature. It is disclosed that Ni2Si can be formed by an annealing process in a range of 300° C. to 350° C., that NiSi can be formed by an annealing process in a range of 350° C. to 650° C., and that NiSi2 can be formed by an annealing process of 650° C. or more. The formation method has features in that a metal film is deposited in a region on which a silicide layer is to be formed and that desired characteristics of a silicide composition are obtained by the temperature of subsequent annealing.
Furthermore, Appl. Phys. Lett., Vol. 74, No. 21, 24 May 1999, p. 3137 (hereinafter referred to as Non-patent Document 2) and Mater. Res. Soc. Symp. Proc. 320, 1994, p. 221 (hereinafter referred to as Non-patent Document 3) disclose supplying Ni, Co, or Fe onto a silicon substrate at a low rate (low supply rate) by using MBE or a vapor deposition method to form NiSi2, CoSi2, or FeSi2 directly on the silicon substrate. Use of a formation method disclosed by those documents has advantages in that a silicide layer having a Si-rich composition can be formed at a temperature lower than that in the method described by Non-patent Document 1.
Moreover, Japanese laid-open patent publication No. 10-144625 (hereinafter referred to as Patent Document 1) discloses a method of applying titanium onto a silicon substrate by a chemical vapor deposition method (CVD) using high-frequency plasma to form a titanium silicide (TiSi2) layer having C54 structure. The features of the technology have advantages in that an annealing process can be omitted because a silicide layer can be formed directly as with Non-patent Document 2.
Furthermore, Japanese laid-open patent publication No. 8-97249 (hereinafter referred to as Patent Document 2) and Japanese laid-open patent publication No. 7-297136 (hereinafter referred to as Patent Document 3) disclose a method of introducing a titanium tetrachloride gas and a hydrogen gas onto a silicon substrate and forming a titanium silicide (TiSi2) layer having C54 structure by a CVD method using plasma excitation with electron cyclotron resonance, helicon wave, or ECR. The features of this technology have advantages in that an annealing process can be omitted because a silicide layer can be formed directly in a similar manner being described in Patent Document 1.
Moreover, Japanese laid-open patent publication No. 2000-58484 (hereinafter referred to as Patent Document 4) discloses a method of forming a titanium silicide layer on a silicon substrate by a plasma CVD method using (1) titanium tetrachloride and a hydrogen gas or (2) titanium tetrachloride, a silane gas, and a hydrogen gas. Furthermore, Japanese laid-open patent publication No. 8-283944 (hereinafter referred to as Patent Document 5) discloses a method which includes using titanium tetrachloride and a silane gas as a raw material gas, adding hydrogen fluoride to the raw material gas, and forming a titanium silicide film (TiSi2) on a silicon substrate by a CVD method.
Furthermore, Japanese laid-open patent publication No. 2003-328130 (hereinafter referred to as Patent Document 6), Japanese laid-open patent publication No. 2005-93732 (hereinafter referred to as Patent Document 7), and Non-patent Document 3 describe a method of forming a nickel silicide film on a silicon substrate by a CVD method by the use of a material containing Ni and a material containing Si.
Furthermore, Extended Abstracts of International Conference on Solid State Devices and Materials 2005, p. 508 (hereinafter referred to as Non-patent Document 4) describes that a nickel silicide film is formed by a CVD method using Ni(PF3)4 as a raw material gas containing Ni and Si3H8 as a raw material gas containing Si and that the composition of the nickel silicide film can be changed by the amount of Si3H8 supplied.
Moreover, U.S. Pat. No. 5,459,099 (hereinafter referred to as Patent Document 8) discloses deposition of Pt by a CVD method using Pt(PF3)4 as a metal material gas, and also describes that a Pt film is formed by supplying a raw material of Pt(PF3)4 onto a silicon substrate heated to 300° C. or less and that a deposition rate of Pt is increased at temperatures higher than 300° C. while a platinum silicide is simultaneously formed.